diff --git a/src/backend/itanium.rs b/src/backend/itanium.rs
index baea095..f579336 100644
--- a/src/backend/itanium.rs
+++ b/src/backend/itanium.rs
@@ -108,7 +108,9 @@ unsafe impl ThrowByPointer for ActiveBackend {
     }
 }
 
-#[repr(C, align(16))]
+#[repr(C)]
+#[cfg_attr(target_pointer_width = "32", repr(align(8)))]
+#[cfg_attr(target_pointer_width = "64", repr(align(16)))]
 pub struct Header {
     class: u64,
     cleanup: Option<unsafe extern "C" fn(i32, *mut Header)>,